Temperature control of crystals used in optical oscillators

Abstract

A crystal, which is mounted in a rotatable support for use in tuning the wavelength of an optical parametric oscillator, is maintained at a desired temperature by positioning a heating sleeve to thermally coupled to the crystal and its support in such a way that the crystal is still free to rotate. The heating sleeve has an embedded heating element for connecting to an electronic controller whose dynamic output response matches the dynamic temperature characteristics of the combination of components including the crystal, it rotatable holder and the heating sleeve, so as to quickly stabilize changes in the crystal temperature with a minimum amount of overshoot.

That which is claimed is: 
     
       1. A method of controlling temperature of a crystal mounted in a rotatable support, said method comprising: thermally coupling said crystal and its rotatable support to a heating sleeve having a heating element, wherein the coupling is accomplished in such a way that the crystal is still free to rotate;   connecting an electronic controller to said heating element; and   matching the dynamic response of said electronic controller and the dynamic temperature characteristics of the combination of components including said heating sleeve, said crystal and said rotatable support.   
     
     
       2. A method in accordance with claim 1 wherein said electronic controller includes a voltage comparator section, a voltage gain section, a power amplifier section and a compensating lead network and wherein said step of matching the dynamic response of said electronic controller and the dynamic temperature characteristics of the combination of components comprises: determining the values of voltage gain, power gain and a time constant for said lead network while said controller is operatively connected to said heating element.   
     
     
       3. A method in accordance with claim 2 wherein said time constant for said lead network is about seven seconds. 
     
     
       4. A method in accordance with claim 3 wherein said heating sleeve is constructed of aluminum and has overall dimensions of about 2"×1"×0.8", and the available power for heating said heating sleeve is about 3.5 watts said method additionally comprising: maintaining the temperature of said crystal substantially above ambient temperature.   
     
     
       5. A method of generating tunable infrared radiation in the 3-5 micrometer range in an optical parametric oscillator employing a crystal mounted in a rotatable support, said method comprising: surrounding at least 3 faces of said crystal with a heating sleeve having a heating element in such a way that the crystal is still free to rotate;   connecting an electronic controller to said heating element;   matching the dynamic response of said electronic controller with the dynamic temperature characteristics of the combination of components including said heating sleeve, said crystal and said rotatable support;   pumping said crystal by a laser operating substantially at 1.064 micrometers in a direction substantially normal to the optic axis of said crystal to produce shifted infrared light in the 3-5 micrometer range; and   turning the frequency of said shifted infrared light by adjusting the mechanical angle at which the incoming laser light strikes the crystal.   
     
     
       6. A method in accordance with claim 5 wherein said electronic controller includes a voltage comparator section, a voltage gain section, a power amplifier section and a compensating lead network and wherein said step of matching a dynamic response of said electronic controller and the dynamic temperature characteristics of the combination of components comprises: determining the values of voltage gain, power gain and a time constant for said lead network while said controller is operatively connected to said heating element.   
     
     
       7. A method in accordance with claim 6 wherein said time constant for the lead network is about seven seconds. 
     
     
       8. A method in accordance with claim 7 wherein said heating sleeve is constructed of aluminum and has overall dimensions of about 2"×1"×0.8", and the available power for heating said heating sleeve is about 3.5 watt said method additionally comprising: maintaining the temperature of said crystal substantially above ambient temperature.   
     
     
       9. Apparatus for controlling the temperature of a crystal mounted in a rotatable support, said apparatus comprising: a generally rectangular heating sleeve having a slot for mating with at least 3 faces of said rotatable support;   a heating element embedded in said heating sleeve;   a thermistor embedded in said heating sleeve;   an electronic controller for connecting to said heating element and said thermistor, said controller having a dynamic response characteristics matched to the dynamic temperature characteristics of the combination of components including said crystal, said rotatable support and said heating sleeve.   
     
     
       10. Apparatus in accordance with claim 9 wherein said controller comprises a voltage comparator section, a voltage gain section, a power amplifier section and a compensating lead network. 
     
     
       11. Apparatus in accordance with claim 10 wherein said lead network includes a resistor and a capacitor electrically connected in parallel and having component values for providing a time constant for said lead network of about seven seconds. 
     
     
       12. Apparatus in accordance with claim 11 wherein said crystal is a lithium niobate crystal employed in an optical parametric oscillator for generating infrared radiation in the 3-5 micrometer range. 
     
     
       13. Apparatus in accordance with claim 12 additionally comprising: a laser light transmitting infrared radiation at a wavelength of 1.064 micrometers; and   means for pumping said crystal with said laser light in a direction substantially normal to the optic axis of said crystal to produce radiation in the three-five micrometer range.   
     
     
       14. Apparatus in accordance with claim 13 additionally comprising: means for rotating said crystal wherein the wavelength of infrared radiation in the 3-5 micrometer range is tuned by adjusting the mechanical angle at which the incoming laser light strikes said crystal.   
     
     
       15. Apparatus in accordance with claim 9 wherein said heating sleeve comprises an aluminum channel having overall dimensions of about 2"×1"×0.8", and said heating element comprises a plurality of electrically series connected resistors.